1. Field of the Invention
The invention relates to a power converting device, and more particularly to an AC-to-DC power converting device.
2. Description of the Related Art
FIG. 1 illustrates a conventional power converting device for converting an AC input voltage (vi) supplied by an external power source 100′ to a DC output voltage (Vo) that is adapted for driving an LED module 200′ that serves as a load. The conventional power converting device includes a filter 10, a full-bridge rectifier 11, a power factor corrector 12, and a step-down converter 13.
The filter 10 is coupled to the external power source 100′, and receives the AC input voltage (vi) for filtering the AC input voltage (vi) to eliminate electromagnetic interference.
The full-bridge rectifier 11 has an input side coupled to the filter 10 for receiving the AC input voltage (vi) filtered by the filter 10, and an output side. The rectifier 11 rectifies the AC input voltage (vi) to output a rectified voltage at the output side.
The power factor corrector 12 is coupled to the output side of the rectifier 11 for receiving the rectified voltage to output a boosted voltage. The power factor corrector 12 includes an inductor (L), a first switch 121, a capacitor (C), a second switch 122 and a third switch 123. The first switch 121 is operable to enable the inductor (L) to store energy or release energy. The second and third switches 122, 123 have zero-voltage switching characteristics, and are operable so that the power factor corrector 12 outputs the boosted voltage to the step-down converter 13.
The step-down converter 13 is coupled to the power factor corrector 12 and receives the boosted voltage from the power factor corrector 12 for reducing the boosted voltage to output the DC output voltage (Vo).
The following are some of the drawbacks of the conventional power converting device:
1. The first switch 121 of the power factor corrector 12 is required to have a high endurance voltage such that a relatively large conducting impedance is exhibited by the first switch 121.
2. A relatively large current flows through the inductor (L) of the power factor corrector 12. Therefore, the inductor (L) has increased power consumption, and a relatively large volume.
3. There are three switches 121, 122, 123 required in the conventional power converting device.
4. Zero-voltage switching characteristics of the second and third switches 122, 123 are associated with the load. When the load is extremely small, an extremely small resonant current generated in the power factor corrector 12 to flow through the second and third switches 122, 123 cannot eliminate energy stored in parasitic capacitances of the second and third switches 122, 123. Therefore, zero-voltage switching of the second and third switches 122, 123 cannot be attained.